Front hood assembly

ABSTRACT

A front hood assembly has a front hood of a motor vehicle that is hinged to the chassis of the motor vehicle via at least one hinge, said front hood being lockable via at least one hood lock. The hinge comprises means for displacing a joint depending on the vehicle speed to an upper or a lower position, independent of whether a collision with a pedestrian has taken place or not. The assembly provides a protection for pedestrians that is technically feasible and can be implemented at low cost. In a method for actuating the front hood of a motor vehicle depending on the vehicle speed, the front hood is displaced into a lifted position at least in the area of its hinges if a lower threshold value of the vehicle speed is exceeded or if the vehicle speed falls below an upper threshold value.

BACKGROUND OF THE INVENTION

The invention relates to a front-hood arrangement wherein a front hoodof a vehicle is coupled via a hinge to the frame of a vehicle, whichfront hood can also be closed by means of at least one hood lock. Theinvention also relates to a method for actuating the front hood of avehicle as a function of the vehicle speed.

By now, numerous safety devices, such as airbags and the like, forpassengers in automobiles are known from practical applications. Bycontrast, protective measures for pedestrians who are hit by the frontend of a passenger automobile have to date scarcely been proposed orimplemented in practice. Accidents involving pedestrians which takeplace at speeds of up to 60 km/h have proven particularly problematical,since, if the pedestrian is hit head-on, his head often strikes theengine hood of the passenger automobile, and the pedestrian dies fromhis injuries. The seriousness of the injury results from the fact thatalthough the front or engine hood, which is usually formed from thinmetal sheet, would tend to bend, it then strikes parts which arearranged beneath the engine hood and in practice cannot be deformed orcan only be deformed with difficulty, such as the engine block, thesuspension-leg carrier, the air filter, the valve cover or the frameside and cross members of the vehicle. It would be desirable if theconsequences of an impact in particular of the head of a pedestriancould be made less severe. By contrast, at speeds of over 60 km/h, thepedestrian, after he has been hit, is thrown over the vehicle.

DE-C-29 22 893 proposes that the engine hood and the wing, in the regionof the joint formed between these two parts, be supported, by means ofenergy-absorbing U-sections which run along the two parts, on bodycomponents, and in the event of a collision these U-sections convert theimpact into deformation energy. A first drawback of this arrangement isthat considerable forces have to act on the sections in order to bendthem. Moreover, these otherwise useless U-sections are expensive toprocure and difficult to fit.

DE-A-27 37 876 describes an impact protection device which uses aprestressed pivot flap to displace a mesh-like absorption element out ofan at-rest position, in which the mesh rests substantially on the fronthood, into an absorbing position, which runs substantially in front ofthe windshield of the automobile. This device is used more to protectthe windshield than the pedestrian from an excessively hard impact onthe front hood. Moreover, any contact with the sensor which triggers thepivoting movement and is integrated in the front bumper can cause themesh to be triggered, with the result that a whole range of situationsarise in which the mesh completely blinds the driver.

DE-A-28 41 315 describes a safety device in which, in reaction to asignal from a sensor arranged at the front of a vehicle, to detect acollision with a pedestrian, the front hood is displaced out of anat-rest position into an impact position, which is raised with respectto the at-rest position, by a piston-cylinder unit, the displacementbeing effected by an energy store. During the raising operation, thefront hood is pivoted about a horizontal pivot pin which is arranged atthe front of the vehicle.

DE-A-197 10 417 describes an arrangement for lifting the front hood inwhich pivoting about a horizontal pivot pin arranged at the front of thevehicle is triggered by the same pneumatic spring which also assistswith the raising of the front hood which is coupled to the other end.

DE-A-197 21 565 describes a safety device on motor vehicles for raisingthe front hood in which the raising of the front hood takes place in aspeed-dependent manner by means of a mechanism which is integral withthe hood lock. For this purpose, either the unlocking of the lock whichis acted on by a compression spring, which for safety reasons isnormally triggered from the driver's compartment, is triggered by asensor which is triggered by an impact, or alternatively, particularlyat relatively high speeds, a piston-cylinder unit which is integrated inthe catch bolt of the hood lock is expanded by a propelling charge. Afirst drawback of this arrangement is that the force required to closethe front hood must not exceed a defined threshold, in order to allowthe driver to close the front hood with ease. Since the forces whichstrike in the event of an accident involving a person are considerable,the front hood is pressed down rapidly, and the known injuries occur, inparticular in the region of the head. Providing a propelling charge inorder to expand a piston-cylinder unit also causes problems, since theservice life of this charge, in particular in a relatively unprotectedarrangement, is limited, and the charge is difficult to exchange.Moreover, there is a risk of the compression spring and thepiston-cylinder unit being triggered simultaneously, with the resultthat the opening of the front hood would become so great that the airstream would bring the hood into contact with the windshield, thuspreventing the driver from being able to see.

DE-A-27 11 338 describes a device for damping the impact of apedestrian, in which an airbag is arranged in the region of the cowl,the filling of which airbag is triggered by a sensor signal. In thiscase, the airbag may be arranged in such a way that, at the same time,it raises a part of the front hood; to do this it overcomes a springforce which preloads two links, which are connected to one another via arotation point and one of which is arranged rotatably on the front hoodand the other of which is arranged rotatably on a fixed part of themotor vehicle, into an angled position. Furthermore, it is proposed toarrange resilient profiled bodies in strip form in the manner of a sealbetween hood and side parts, in order in this way to provide furtherprotection in the event of an impact.

DE-A-27 11 339 describes a front hood which is coupled at the front sideand in which the coupling is designed to be resilient, in such a mannerthat it allows horizontal displacement of the front hood through theimpact of a pedestrian, the front hood which is displaced toward therear being connected at the rear side to one end of a rigid lockingelement, the other end of which, in the event of displacement of thefront hood toward the rear, is displaced upward and toward the rear in aguide curve in such a manner that the front hood executes an upwardmovement. This lifting only takes place if horizontal displacement ofthe front hood has actually occurred, which is not always the case, forexample, in the event of impacts of children.

EP-A-0 509 690 describes a front hood, which at its front side iscoupled to the vehicle structure in such a manner that, as a result ofan impact, the front hood is displaced toward the rear, the closure orpivot means arranged at the rear side, as a result of a movement of thefront hood toward the rear, triggering an upward pivoting movement ofthe front hood, so that the deformation travel of the hood is increasedin the event of the impact of a pedestrian. The pivoting movement isguided, for example, by a four joint hinge, which is otherwise used topivot the front hood when it is desired to release access to the engineand other parts. In this case too, the front hood is only lifted in theevent of very substantial displacement of the front hood, while a weakimpact does not displace the front hood toward the rear and thereforeupward.

DE-A-197 12 961 describes the arrangement of a front hood on a vehiclein which a hinge is arranged on a hinge mount, which hinge mount, in theevent of a collision with a pedestrian, is pivoted upward in order toraise the front hood. A problem of this arrangement is that the hoodlock for the front hood defines a pivot axis which does not allowoptional displacement of the hinge mount, and consequently the hingemount described is, for example, blocked.

EP-A-0 926 018, which was published after the priority date of thepresent application, describes a front hood which permanently lies in alowered position and, in the event of a collision, is extended if thevehicle is moving at an appropriate speed.

SUMMARY OF THE INVENTION

WO-A-97 18 108 describes a front-hood arrangement in which a collisionwith a pedestrian is detected by means of an impact sensor, andimpact-damping means in the form of an airbag are triggered if, duringthe collision, the vehicle speed moves within a predetermined range.However, a problem with an arrangement of this type is that of providingan airbag in the outside region of the engine hood, since there it isexposed to external influences, including influences of weather, such asinsolation, wet and frost, and therefore it cannot be guaranteed tooperate throughout the entire service life of an automobile, and afurther drawback is the tightness of reaction time.

JP-A-10 258 774 or JP-A-09 315 266 relates to front-hood arrangements inwhich the front hood is raised as a result of a collision with apedestrian being detected and is otherwise retained in a loweredposition. A particular problem of this solution is that the reactiontimes passing between a collision and its detection and the processingof the commands to trigger the device to raise the front hood aregenerally too long to guarantee that the front hood is actuated in goodtime. Furthermore, the front hood is also extended if the impactdetectors respond, for example, in the event of a parking incident or ifan obstacle is driven into at high speed.

JP-A-10 194 158 describes a complex and expensive design of a front-hoodarrangement in which the front hood is raised when a collision isdetected, for which purpose a sensor is provided in the front part ofthe vehicle and is read by means of a control unit which also actuates apiston-cylinder unit in order to raise the front hood. The actuatingdevice is only extended when a collision of this type is detected. Inthis case, at the same time, the vehicle speed and acceleration are usedto determine whether this is a collision with an object. To this extent,the assumption is that the account taken of the vehicle speed is usedonly to establish whether a collision has occurred, and it is not at thesame time the case that a speed range limits the raising of the fronthood. In this context, it should be noted that, to ensure a passengerimpact function, the front hood, if it is desired to restrict theraising of the front hood to an impact situation, must respond withinless than one second, preferably less than half a second. Although thereare now high-performance computers, it is nevertheless not ensured thatthe front hood will be completely raised before the head of a pedestrianstrikes it. This is the case in particular if the impact takes place ina corner region and therefore, on account of the different resistance onthe two actuating devices, tilting is possible, which impedes completeraising of the front hood.

Overall, as yet no solution has been proposed which proposes aninexpensive arrangement, which can be readily restored after use andwhich is so well developed that it could be used in mass-producedvehicles.

It is the object of the invention to propose a front-hood arrangementand a method that supply pedestrian protection that can be achievedinexpensively and on an industrial scale.

This object is achieved for the front-hood arrangement described at thebeginning, according to the invention, in that the hinge has means fordisplacing a joint, as a function of the speed of the vehicle, into anupper or a lower position, independently of an impact of a pedestrian.This object is achieved for the method described at the beginning,according to the invention, in that the front hood, at least in theregion of its hinges, is displaced into a raised position in the eventof exceeding a lower threshold or in the event of undershooting an upperthreshold for the speed.

DETAILED DESCRIPTION OF THE INVENTION

The arrangement according to the invention enables the front hood to beraised in those speed ranges within which the impact of a pedestrian isparticularly dangerous. By contrast, when the vehicle is stationary ortraveling at slow speeds, such as when parking, when visibility isparticularly important, and at high speeds, at which the aerodynamics ofthe front hood plays a major role, the hood is in a lowered position,since in both cases the impact of a pedestrian would not lead to hishead striking the front-hood. For this purpose, the unit which effectsthe displacement and which preferably executes a linear movementexpediently acts directly on the joint which forms the rotation point ofthe hood bearing, so that pivoting of the front hood about the hood lockover a corresponding radius is ensured.

In particular, it is possible to design the actuating device as apiston-cylinder unit which can be extended and retracted slowly, while ahigh-speed device has to be provided in a system which has to betriggered. This can generally only be designed as a single-use device bymeans of a propelling charge or the like, and requires expensive refitoperations for each false alarm. By contrast, the method according tothe invention or the front-hood arrangement according to the inventionallows the automobile to be used further without problems if contactoccurs with the bumper when, for example, the automobile is beingparked.

The front hood is preferably raised at speeds of over 10 km/h and islowered back into its starting position at speeds of over 50 km/h, whilethe raising also takes place when the speed falls below 45 km/h and thefront hood is lowered again when the speed falls below 5 km/h. It isalso possible for the front hood only to be lowered once the motorvehicle is stationary, in order to prevent it from constantly moving upand down in city traffic. Moreover, a delay circuit may be provided,with which the lowering of the front hood is only triggered when thevehicle has been stationary for more than an adjustable threshold of,for example, 5 seconds.

For displacement of the joint, there is preferably a piston-cylinderunit arranged on each side of the vehicle frame side member, thepiston-side end of which unit bears the joint and the cylinder of whichis in each case fixed to one of the frame side members. This ispreferably a pneumatically driven piston-cylinder unit which can becompressed in a similar manner to a pneumatic spring and therefore, inthe event of a collision with a pedestrian, is also able to convertimpact energy into compression and therefore contributes to reducing theconsequences of the impact, in particular on the head part of apedestrian. The pneumatic piston-cylinder unit can expediently besupplied via other equipment in the vehicle which also requires orgenerates reduced pressure, without tall incurring major costs. Theactivation unit of the piston-cylinder unit can preferably be switchedover in order to be able to act on or empty on both sides of the pistonand accordingly to increase the speed of displacement of the piston-cylinder unit. Furthermore, the spring assemblies can be provided toassist the piston-cylinder unit.

The speed is measured by means of a speed sensor and is transmitted viaelectronic commands, for example in a data bus line, from a centralcontrol unit to the lifting means, for example the pneumaticpiston-cylinder unit. The displacement of the joint is triggered inresponse to the preset thresholds being exceeded or undershot. It isadditionally possible to lock the lifting member at relatively highspeeds, in order to increase the rigidity of the vehicle in the event ofa head-on collision with another vehicle.

Expediently, as well as the two lifting units for the joints of thefront hood, at the front side thereof a further lifting unit is assignedto the hood lock, and this further lifting unit also raises the fronthood in the region of the hood lock; this raising may not be as strong,but is nevertheless perceptible. This is expedient in particular if thehood lock is arranged in the region of the A-pillars of the vehicle orin the region of the windshield, since substantial raising of front-sidejoints would only slightly cushion the impact of the human head in thevicinity of the windshield. Expediently, however, the front-hoodarrangement will be provided with joints arranged at the rear side ofthe front hood and a hood lock arranged at the front side of the fronthood, so that the pivoting of the front hood takes place substantiallyin the opposite direction to the assumed impact of the head of apedestrian who has been struck.

Further advantages and features of the invention will emerge from thefollowing description and from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below on the basis of anexemplary embodiment and with reference to the drawing.

FIG. 1 diagrammatically depicts the front part of a motor vehicle with afront-hood arrangement according to the invention.

As can be seen in FIG. 1, the front hood 1 is locked at its front side 2by means of a hood lock 3, while two hinges 4 which are arranged in thecorners of the rear side of the front hood 1 allow pivoting about anaxis of a joint 6 which runs substantially horizontally andperpendicular to the direction of travel. The piston-side end of apiston-cylinder unit 15, which can be extended or retracted in reactionto the speed of the vehicle, acts on the joint 6. Alternatively, otherlifting motors may also be suitable. In this case, the rotatablecoupling of the joint 6 causes the hood lock 3 to produce a pivot axisfor raising the front hood 1 in the direction of the arrow P.

The speed of the vehicle is measured, for example, using a sensor on thefront axle 16, measurement devices of this type being known andgenerally also feeding the speedometer in the vehicle with suitableinformation. A control unit of the piston-cylinder unit 15 reacts to thespeed or the speed changes and, in the event of a speed of, for example,10 or 15 km/h being exceeded, raises the front hood 1, while if a speedof, for example, 55 km/h is exceeded, although this may also be matchedto the local speed limit, if appropriate plus an added tolerance, thefront hood 1 is lowered again. The front hood 1 is raised again if thespeed falls below, for example, 40 km/h, and triggering can also beprovided in the event of strong braking deceleration of the vehicle.When the vehicle is stationary or traveling slowly at, for example, 5km/h, at which speed striking a pedestrian could not have fatalconsequences, the front hood 1 is lowered again, in order to increasethe driver's view. An electronic holding circuit prevents the front hood1 from being constantly raised and lowered, for example in city traffic,through the fact that, by way of example, a time of 5 or 10 secondswithin which the lowering conditions for the front hood 1 are satisfiedmust elapse before the lowering of the front hood is triggered. Althoughthis extends the time for which the driver's view may be restricted, atthe same time it prevents the front hood from being constantly extendedand retracted, which could irritate the driver.

It is possible to refine the front-hood arrangement according to theinvention in such a manner that, in addition to the speed data, theacceleration data are also taken into account in the duration which ispredetermined by the holding circuit, i.e. in the event of suddenbraking the front hood 1 is extended even at a relatively high speed, orthe front hood is retracted in the event of sudden acceleration.

The invention has been explained above with reference to an exemplaryembodiment in which the piston-side end of the piston-cylinder unit 15acts directly on the joint 6 which, at the same time, defines the pivotaxis when the front hood 1 is opened up to provide access to the engine.Alternatively, it is possible to provide this coupling by means of anintermediate member which itself is designed in a particular way so asto be deformed in the event of an impact from a human body and which, inthe retracted state of the front hood 1, is guided or mounted in such amanner that the axial rigidity of the vehicle, which is of importancefor its crash behavior, is not impaired.

What is claimed is:
 1. A front hood assembly for attachment to avehicle, comprising a front hood; at least one hood lock for closingsaid front hood, and a hinge for coupling said front hood to a frame ofsaid vehicle, said hinge comprising means for displacing a joint, as afunction of the speed of the vehicle, into an upper or a lower position,independently of an impact of said vehicle with a pedestrian.
 2. Thefront hood assembly as claimed in claim 1, wherein said means fordisplacing said front hood are triggered in the event of a thresholdbeing undershot, and the displacement means are returned again in theevent of a second threshold being reached, wherein the thresholds arespeeds of said vehicle.
 3. The front hood assembly as claimed in claim1, wherein said hinges are arranged at the rear part of said front hoodand said at least one hood lock is arranged in the front part of thefront hood.
 4. The method as claimed in claim 1, wherein said means fordisplacing the joint is for displacing the joint into the upper and thelower position, independently of said impact.
 5. A front hood assemblyfor attachment to a vehicle, comprising a front hood; and a hinge forcoupling said front hood to a frame of said vehicle, said hingecomprising means for displacing a joint, as a function of the speed ofthe vehicle, into an upper or a lower position, independently of animpact of said vehicle with a pedestrian, wherein the displacement ofsaid front hood is triggered in the event of a lower threshold beingexceeded, and is returned again in the event of an upper threshold,which is higher than the lower threshold, being exceeded, wherein thethresholds are speeds of said vehicle.
 6. The front hood assembly asclaimed in claim 5, wherein said means for displacing said front hoodcomprises a linear lifting drive which acts in an articulated manner onsaid joint.
 7. The front hood assembly as claimed in claim 6, whereinsaid linear lifting drive is designed as a piston-cylinder unit.
 8. Thefront hood assembly as claimed in claim 7, wherein said piston-cylinderunit is pneumatically actuatable.
 9. The front hood assembly as claimedin claim 7, wherein said piston-cylinder unit can be changed to executea linear movement.
 10. The front hood assembly as claimed in claim 5,wherein said means for displacing a joint comprises means for displacingsaid front hood, and wherein said means for displacing said front hoodare actuated in response to signals from a control unit.
 11. The fronthood assembly as claimed in claim 5, further comprising a hood lock andmeans for displacing said hood lock into a raised position, means fordisplacing said hood lock being actuatable in accordance with thedisplacement of said hinge.
 12. The front hood assembly as claimed inclaim 5, wherein a minimum time is provided prior to the return movementof the displacement means.
 13. A method for actuating the front hood ofa vehicle as a function of the vehicle's speed, wherein said vehiclecomprises a frame, a front hood, a hinge for coupling said front hood tosaid frame, and means for displacing said front hood into an upper or alower position, the method comprising the steps of measuring the speedof said vehicle, comparing said measured speed to a preset lowerthreshold of vehicle speed and to a preset upper threshold of vehiclespeed, and in the event of said vehicle exceeding said lower thresholdor in the event of said vehicle undershooting said upper threshold,displacing said front hood, at least in the region of its hinges, into araised position.
 14. The method as claimed in claim 12, wherein saidvehicle further comprises at least one hood lock for closing said fronthood, and wherein said step of displacing said front hood comprisesdisplacing said front hood into a raised position in the region of saidhood lock.
 15. The method as claimed in claim 12, wherein said means fordisplacing said front hood into an upper or a lower position comprisespneumatic piston-cylinder units, and wherein said step of displacingsaid front hood comprises activation of pneumatic piston-cylinder units.16. The method as claimed in claim 12, wherein said step of displacingsaid front hood occurs after said vehicle has exceeded said lowerthreshold for a preset minimum amount of time or after said vehicle hasundershot said upper threshold for a preset minimum amount of time.